提升钢丝绳动态分析的分段线性化解法

本文在研究提升机绳系动态特性过程中,建立了一类非齐次边界条件混合问题的波动方程;应用离散化方法将非齐次项分段线性化,得到了该类波动方程的半解析解.     

Optimality of a Threshold Policy in theM/M/ queue with repeated vacations

Consider anM/M/1 queueing system with server vacations where the server is turned off as soon as the queue gets empty. We assume that the vacation durations form a sequence of i.i.d. random variables with exponential distribution. At the end of a vacation period, the server may either be turned on if the queue is non empty or take another vacation. The following costs are incurred: a holding cost ofh per unit of time and per customer in the system and a fixed cost of each time the server is turned on. We show that there exists a threshold policy that minimizes the long-run average cost criterion. The approach we use was first proposed in Blanc et al. (1990) and enables us to determine explicitly the optimal threshold and the optimal long-run average cost in terms of the model parameters.     

Optimal production control of a dynamic two-product manufacturing system with setup costs and setup times

This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically.     

Computational experience with general equilibrium problems

We report on computational experience with an implementation of three algorithms for the general economic equilibrium problem. As a result we get that the projection algorithm for variational inequalities increases the size of solvable models by a factor of 5–10 in comparison with the classical homotopy method. As a third approach we implemented a simulated annealing heuristic which might be suitable to estimate equilibria for very large models.Supported by the German Research Association (Deutsche Forschungsgemeinschaft, SFB 303).     

我国等离子体工艺研究进展

扼要综述了我国等离子体材料工艺研究的新近进展。内容包括：热等离子体源,等离子冶金、化工,超细粉合成,喷涂;低气压非平衡等离子体源,镀膜,表面改性,等离子浸没离子注入,电晕放电,介质阻挡放电,滑动弧等及其应用,当前,各类薄膜制备和表面改性的研究工作更为活跃。     

三线圈超导磁体在脉冲电流下的动力稳定性分析

对于聚变反应堆中超导载流磁体在稳态电流基础上受到脉冲电流影响时的动力稳定性给出了定量分析方法。结合其超导载流磁体的实验结构,给出了超导磁体在不同稳态工作电流（即低于稳态的磁弹性人稳临界电流）作用下受到矩形脉冲电流作用 磁弹性动力响应的数值模拟结果。在此基础上,给出了关于稳态工作电流、脉冲电流强度和脉冲持续时间等参数的磁弹性动力稳定性参数范围。     

Dynamic glottal pressures in an excised hemilarynx model

During phonation, air pressures act upon the vocal folds to help maintain their oscillation. The air pressures vary dynamically along the medial surface of the vocal folds, although no live human or excised studies have shown how those pressure profiles vary in time. The purpose of this study was to examine time-dependent glottal pressure profiles using a canine hemilarynx approach. The larynx tissue was cut in the midsaggital plane from the top to about 5 mm below the vocal folds. The right half was replaced with a Plexiglas pane with imbedded pressure taps. Simultaneous recordings were made of glottal pressure signals, subglottal pressure, particle velocity, and average airflow at various levels of adduction. The data indicate that the pressures in the glottis (on the Plexiglas) vary both vertically and longitudinally throughout the phonatory cycle. Pressures vary most widely near the location of maximum vibratory amplitude, and can include negative pressures during a portion of the cycle. Pressures anterior and posterior to the maximum amplitude location may have less variation and may remain positive throughout the cycle, giving rise to a new concept called dynamic bidirectional pressure gradients in the glottis. This is an important concept that may relate strongly to tissue health as well as basic oscillatory mechanics.     

Magnetization dynamics below of EuO and EuS

Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities have been investigated by means of a broad-band reflectometer operating from 0.1 GHz to 40 GHz. For internal magnetic fields larger than the anisotropy fields H A ( T ) of both materials, their static susceptibilities exhibit a -divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. displays a Lorentzian shape the damping frequency of which obeys scaling in terms of .The scaling function agrees quantitatively with work by Frey and Schwabl [#!FS88!#] for dipolar Heisenberg ferromagnets at temperatures above T_c. Building upon their approach, the resonance frequency of the Lorentzian can be related to a memory effect in the damping determined by the large value of the relaxation rate of the longitudinal magnetization fluctuations . For EuS, this relation is substantiated directly by inelastic neutron scattering. All these features reveal the hitherto uncovered importance of the dipolar anisotropic fluctuations below T_c of ferromagnets. Received: 4 March 1998 / Accepted: 12 May 1998     

Magnetic relaxation phenomena in a CuMn spin glass

Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn) spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation. Received 27 October 1998 and Received in final form 30 November 1998     

How to measure energy dissipation in dynamic mode atomic force microscopy

When studying a mechanical system like an atomic force microscope (AFM) in dynamic mode it is intuitive and instructive to analyse the forces involved in tip–sample interaction. A different but complementary approach is based on analysing the energy that is dissipated when the tip periodically interacts with the sample surface. This method does not require solving the differential equation of motion for the oscillating cantilever, but is based entirely on the analysis of the energy flow in and out of the dynamic system. Therefore the problem of finding a realistic model to describe the tip–sample interaction in terms of non-linear force–distance dependencies and damping effects is omitted. Instead, it is possible to determine the energy dissipated by the tip–sample interaction directly by measuring such quantities as oscillation amplitude, frequency, phase shift and drive amplitude. The method proved to be important when interpreting phase data obtained in tapping mode, but is also applicable to a variety of scanning probe microscopes operating in different dynamic modes. Additional electronics were designed to allow a direct mapping of local energy dissipation while scanning a sample surface. By applying this technique to the cross-section of a polymer blend a material specific contrast was observed.